In semiconductor devices, to prevent the formation of an insulation film of low dielectric constant in the interface between the electrodes and the insulation film it is necessary to use materials which is not oxidized or exhibit metal conductivity when oxidized. The use of ruthenium (Ru) film or ruthenium oxide (RuO2) film as electrode materials of the capacitors which meet such requirement is being studied.
Such films can be formed on wafers by CVD using Ru(EtCP)2 as the raw material, by using an apparatus, e.g., a vertical thermal processing apparatus. Etisanethyl group, and CP is cyclopenthane (C5H4) . Ruthenium film has the property of reflecting light, and when ruthenium film adheres to the inside of a reaction tube, the radiant heat from the heater outside the reaction tube is hindered from reaching the wafer. Resultantly, the temperature of the wafer becomes unstable, and films are released, which is a factor for causing contamination. Accordingly, the inside wall of the reaction tube must be cleaned frequently, e.g., after every one batch of processing, and the cleaning with, e.g., ClF3 gas is being studied.
However, the reaction tube is generally formed of quartz, and the wafer boat is formed of quartz. The use of ClF3 gas has a problem that the ClF3 gas will damage them, and a risk that the ClF3 gas may react with water intruding into the reaction tube from the processing gases or the air, causing HCl or HF to reside on the inside wall of the reaction vessel, the wafer boat etc., and scatter into films on the wafers.
In such circumstances the present invention has been made, and an object of the present invention is to provide a technique of cleaning the interior of a reaction vessel in which ruthenium film or ruthenium oxide film has been formed on objects-to-be-processed efficiently without damaging the reaction vessel and contaminating the objects-to-be-processed.